The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.
The celiac plexus, also known as the solar plexus because of its radiating nerve fibers, is a complex network of nerves located in the abdomen, near where the celiac trunk, superior mesenteric artery, and renal arteries branch from the abdominal aorta. It is behind the stomach and the omental bursa, and in front of the crura of the diaphragm, on the level of the first lumbar vertebra.
A nerve plexus is a plexus of intersecting nerves. A nerve plexus is composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve plexuses, except in the thoracic region, as well as other forms of autonomic plexuses, many of which are a part of the enteric nervous system. The nerves that arise from the plexuses have both sensory and motor functions. These functions include muscle contraction, the maintenance of body coordination and control, and the reaction to sensations such as heat, cold, pain, and pressure. There are several plexuses in the body, including:
The inferior mesenteric plexus is derived chiefly from the aortic plexus.
The renal plexus is a complex network of nerves formed by filaments from the celiac ganglia and plexus, aorticorenal ganglia, lower thoracic splanchnic nerves and first lumbar splanchnic nerve and aortic plexus.
The abdominal aortic plexus is formed by branches derived, on either side, from the celiac plexus and ganglia, and receives filaments from some of the lumbar ganglia.
The superior hypogastric plexus is a plexus of nerves situated on the vertebral bodies anterior to the bifurcation of the abdominal aorta. It bifurcates to form the left and the right hypogastric nerve. The SHP is the continuation of the abdominal aortic plexus.
The celiac ganglia or coeliac ganglia are two large irregularly shaped masses of nerve tissue in the upper abdomen. Part of the sympathetic subdivision of the autonomic nervous system (ANS), the two celiac ganglia are the largest ganglia in the ANS, and they innervate most of the digestive tract.
The sympathetic ganglia, or paravertebral ganglia, are autonomic ganglia of the sympathetic nervous system. Ganglia are 20,000 to 30,000 afferent and efferent nerve cell bodies that run along on either side of the spinal cord. Afferent nerve cell bodies bring information from the body to the brain and spinal cord, while efferent nerve cell bodies bring information from the brain and spinal cord to the rest of the body. The cell bodies create long sympathetic chains that are on either side of the spinal cord. They also form para- or pre-vertebral ganglia of gross anatomy.
The lateral grey column is one of the three grey columns of the spinal cord ; the others being the anterior and posterior grey columns. The lateral grey column is primarily involved with activity in the sympathetic division of the autonomic motor system. It projects to the side as a triangular field in the thoracic and upper lumbar regions of the postero-lateral part of the anterior grey column.
The pelvic portion of each sympathetic trunk is situated in front of the sacrum, medial to the anterior sacral foramina. It consists of four or five small sacral ganglia, connected together by interganglionic cords, and continuous above with the abdominal portion. Below, the two pelvic sympathetic trunks converge, and end on the front of the coccyx in a small ganglion, the ganglion impar, also known as azygos or ganglion of Walther.
Thoracic splanchnic nerves are splanchnic nerves that arise from the sympathetic trunk in the thorax and travel inferiorly to provide sympathetic supply to the abdomen. The nerves contain preganglionic sympathetic fibers and general visceral afferent fibers.
The superior mesenteric plexus is a continuation of the lower part of the celiac plexus, receiving a branch from the junction of the right vagus nerve with the plexus.
The superior mesenteric ganglion is a ganglion in the upper part of the superior mesenteric plexus. It lies close to the origin of the superior mesenteric artery.
Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the organs of the pelvic cavity.
Sacral splanchnic nerves are splanchnic nerves that connect the inferior hypogastric plexus to the sympathetic trunk in the pelvis.
The lumbar splanchnic nerves are splanchnic nerves that arise from the lumbar ganglia and travel to an adjacent plexus near the aorta. They originate from L1 and L2. Together with fibres from the aortic plexus, they form the superior hypogastric plexus.
The lumbar ganglia are paravertebral ganglia located in the inferior portion of the sympathetic trunk. The lumbar portion of the sympathetic trunk typically has 4 lumbar ganglia. The lumbar splanchnic nerves arise from the ganglia here, and contribute sympathetic efferent fibers to the nearby plexuses. The first two lumbar ganglia have both white and gray rami communicates.
The following diagram is provided as an overview of and topical guide to the human nervous system:
